There are many processes for extracting metal values from ores in which ores that contain metals such as copper, nickel and cobalt are first leached and are then subjected to selective extraction to recover the various metals in the ore. An example of such a process is the so called, "Cuprion Process" which is disclosed in U.S. Patent application Ser. No. 311,063 entitled "Recovery of Metal Values from Manganese Deep Sea Nodules," filed Dec. 1, 1972, now abandoned in favor of continuation-in-part application Ser. No. 548,430, filed Feb. 10, 1975 the teachings of which are incorporated herein by reference.
A problem which often occurs when treating ores containing copper, nickel and cobalt is that the cobalt can build up to intolerable levels on the organic extractant as other metals are extracted. Indeed, the stripping of cobalt from organic extractant is a problem that has plagued the industry. In connection with the foregoing, the various stripping processes known for stripping cobalt from organic extractants involve conditions under which the organic extractant is partially destroyed. Of course, destroying the organic extractant increases the cost of solvent extraction and should be avoided.
It is generally known that divalent cobalt is readily extracted on to oximes from ammoniacal leach solutions. However, as is stated above, cobalt is not readily stripped from the organic oxime extractant. U.S. Pat. No. 3,276,863 to Drobnick et al, entitled "Separation of Nickel and Cobalt Values Using .alpha.-hydroxy Oximes" teaches that one way to selectively extract nickel from an ammoniacal solution containing cobalt and nickel is to oxidize the cobalt values in the aqueous solution to the trivalent state and then contact the resulting solution with a liquid oxime extractant to extract the nickel values therefrom. Indeed, Column 5, Line 13 et seq. of the Drobnick patent teaches:
"This example shows that as aeration or oxidation period is increased (cobalt oxidized to trivalent state) the percent extraction of nickel increases greatly and the percent cobalt extraction is reduced to substantially negligible amount. Continuation of the aeration period reduces the cobalt extraction to zero and further increases the nickel extraction."
At this point it should be noted that numerous tests have indicated that it is impossible to completely eliminate cobalt extraction when extracting with oximes from ammoniacal leach liquors. Indeed, oxidized cobalt is slowly extracted by oximes. Stated another way, although oxidation reduces the percentage of cobalt that is extracted for a given contact time with a cobalt bearing solution, oxidation does not completely prevent cobalt extraction. This fact creates a considerable problem because extracted cobalt builds up as the organic extractant is continuously recycled and is difficult to strip.
It has been generally assumed that since the divalent species of cobalt is the species which readily extracts, it is the divalent species that is complexed in the organic. In accordance with the present invention, however, it has been discovered that although the divalent cobalt ions readily extract into organics such as oximes, once extracted the cobalt is rapidly oxidized to the trivalent state in the presence of air. The trivalent cobalt complex, which is characteristically dark brown in color, is so stable that it is almost impossible to strip off the organic with dilute mineral acids. However, the divalent cobalt complex, which is characteristically yellow in color when extracted into the organic in the absence of air, is easily stripped off the organic with dilute mineral acids.